Digital type wrist watches incorporating liquid crystals or light emitting diodes to provide the digital read-out are now well known in the art. All such watches, however, normally require a small push button on the side of the watch casing to illuminate the digital display when a person desires to tell the time. Since such operation requires the use of the wearer's other hand, more recent versions of the digital read out wrist watches have incorporated an inertia responsive switch which can be actuated by a flick of the wrist of the wearer to illuminate the display.
In my copending patent application Ser. No. 538,743 filed Jan. 6, 1975 and entitled ACCELERATION/DECELERATION ACTUATING MECHANISM FOR WRIST INSTRUMENTS now U.S. Pat. No. 3,946,173, there is described one of the inertia switches enabling illumination of a digital watch display by a flick of the wrist. The particular inertial switch as shown and described in this copending application incorporates a conducting member in the form of a ball normally held at one end of an elongated hollow switch body by a magnet. Switch contacts at the opposite end of the body are arranged to be bridged by the conducting ball when the wearer's wrist is flicked sufficiently to free the ball from the magnet.
In the mass production of digital watches incorporating an inertia switch of the foregoing type, it is very difficult to maintain uniform action of the particular inertial switch components. This difficulty primarily results from the fact that the magnets while made as uniform as possible do not always provide the same attractive force to the conducting member. Further, slight tolerances in the construction of the magnetic inertia switch body as well as the conducting member in the form of the ball can result in non-uniform action between various successive assemblies incorporated in wrist watches.
In view of the foregoing, a need has arisen to provide some method and means for calibrating each of the inertia switches prior to incorporation in a wrist watch to assure that each of the watches incorporating such switches will operate uniformly; that is, assure that the inertia switch will function in response to flicking or movement of the wearer's wrist. With such a calibrating system, quality control in the mass production of such watches can be assured.